Rotation matrix in the EPSG

I use Proj4j for a WebGIS and I have to create a new ESPG. I try on Qgis to convert coordinates from local system (in Greece) to a world coordinates system. First, I have to do a 2D transformation : 2 translations (Tx ans Ty) and a rotation (Rz) of about 0.58931 radians around the "z axis" (in the plane of the local system) between the local coordinates and the greek coordinates (EGSA87). So I think that the rotation matrix is : [cos(Rz),-sin(Rz);sin(Rz),cos(Rz)] and without the cos and sin I have [0.8313242,-0.5557878;0.5557878,0.8313242] Then, I can reuse the parameters of the EPSG:2100 definition : +proj=tmerc +lat_0=0 +lon_0=24 +k=0.9996 +x_0=500000 +y_0=0 +ellps=GRS80 +towgs84=-199.87,74.79,246.62,0,0,0,0 +units=m +no_defs I think that I can insert the translations (Tx and Ty) in the x_0 and y_0, but I don’t know how to insert the rotation matrix. How can I insert a transformation with a matrix in a new EPSG ? I found on the internet that the “+xform=” command seems good, but I don’t know how to use it. I try : +proj=tmerc +lat_0=0 +lon_0=24 +k=0.9996 +x_0=-869388.894 +y_0=-4260031.458 +xform=[0.8313242,-0.5557878,0.5557878,0.8313242] +ellps=GRS80 +towgs84=-199.87,74.79,246.62,0,0,0,0 +units=m +no_defs But apparently it isn’t a good solution … So, do you know how I can use this command in my new EPSG or where I can find the proj4 documentation ?

Thank you.